1. Field of the Invention
This invention relates to the field of machine tools, and particularly to impact absorbing apparatus for protecting rotary mechanism of machine tools from damage due to overload or sudden impact.
2. Description of the Prior Art
Machine tools commonly incorporate rotary drive or feed mechanism for moving the workpiece relative to a cutting tool. Sometimes, due to the irregularity of configuration or inhomogeneity of the workpiece, substantial impacts and force nonuniformities are brought to bear on the rotary structure of the machine tool, or such forces may be generated by the inadvertent impacting of the workpiece on a stationary obstacle in its path of motion. These forces have been known to damage the machine tool.
More specifically, and referring to FIG. 1, a prior art rotary feed mechanism for a machine tool is shown. A feed shaft 1 is journaled in a radial bearing 2 and a thrust bearing 3, while power from a motor (not shown) is transmitted to the rotary feed shaft by way of a reduction gear 4. A work 5 and a worm wheel 6 respond to the rotation of the feed shaft to impart rotational motion to a portion of the machine tool (not shown) such as a worktable for feeding and rotating a workpiece.
In accordance with this arrangement, when an impact or overload is encountered between the workpiece and the cutting tool, a great deal of force is applied between the teeth of the worm wheel and the worm, and great forces are generated tending to displace the feed shaft in a longitudinal direction. Such forces can result in the breakdown of the bearings holding the feed shaft, or in the gearing constituting the drive between the motor and the worktable.
Some forms of protective apparatus for preventing this damage have been proposed, but none have been as effective as is desired. Previously, structure has been proposed for sensing the buildup of forces in various mechanisms of the machine tool, and for deactuating the power source of the machine tool to prevent damage from overloading or impact.
More recently, however, larger machine tools have been provided, capable of performing work on larger sized workpieces. The greater size of the machine tools and their workpieces has given rise to increased forces generated by overload and impacts than were previously the case. These increased forces, and the corresponding increase in their tendency to damage the machine tool, have elicited a desire for additional apparatus to protect the machine tool from damage resultant on these forces and impacts. Such impacts can result in the failure of the rotary feed mechanism itself, or in breakage of the cutting tool.